These DCT gearboxes are all the rage you know!

[670cc]

DCTs and CVTs are wonderful things. I enjoy the ease of twist and go that the wife and I have on half of our motorcycle/scooter fleet. However, let's not forget that there is an old, experienced lot of motorcyclists out there for which shifting a manual transmission is as automatic as breathing. No conscious thought is involved in operating the clutch and shifter, just as no conscious thought is involved in breathing. Shifting "just happens" as needed either way, whether I think about it or not. So for me, the transmission type is of little importance. I'm in it for the ride: the steering, the balance, the "flow" of the machine down the road.

 

[Normsthename]

It's not going be long before other manufacturers bring out there DCT versions
Here in the UK there has been a major shortage of DCT bikes due to demand.
Some owners have had to wait 4 months from placing an order!

Andy

 

[tapsak4]

In theory, no.

On a dual clutch transmission, most of the time while the bike is in operation, one of the clutches is engaged and one is disengaged. The disengaged clutch's plates are slipping past each other, potentially wearing down and potentially causing friction losses. On a single clutch bike the one clutch spends the vast majority of time engaged, hence there would be less wear.

Well, yes and no

The "other" clutch "slips" only momentarily just prior to engaging and the other one releasing during shifting process.

The next gear - up or down - is mechanically pre-selected only a very short time before it is needed (you can hear the preselection before the clutches switch engagement and the ratio is actually changed). Until that happens all other gears (than the ones actually driving) are disconnected from the power flow thus the slip is only a slight drag.

Attached is a partial schematic of the Getrag 7 speed in the M3 Beemer showing power flow in 1st and 2nd gears. The light blue thingies are "sliding gears" which connect the gears to the shafts when engaged. 7th gear is direct.

I have ordered the Honda manual forthe NCXD - can't wait to see how detailed it is in this area.

Kind regards,

Tapani

-edit: PS Has anyone noticed if the ECU/TCU shifts to neutral if you let the bike idle at stand still for a long time? After how long should I shift to neutral? I've thought about this while sitting at traffic lights

 

[kpinvt]

-edit: PS Has anyone noticed if the ECU/TCU shifts to neutral if you let the bike idle at stand still for a long time? After how long should I shift to neutral? I've thought about this while sitting at traffic lights

I haven't noticed this yet. I don't get to spend more than a few minutes, 5 or so, in traffic here in town. If I stop the bike on the side of the road to take care of something like pulling a camera out of the frunk I set the brake and hit the neutral button.

 

[Fuzzy]

I've never seen mine switch to neutral unless I do it manually.

 

[670cc]

Well, yes and no

The "other" clutch "slips" only momentarily just prior to engaging and the other one releasing during shifting process.

The next gear - up or down - is mechanically pre-selected only a very short time before it is needed (you can hear the preselection before the clutches switch engagement and the ratio is actually changed). Until that happens all other gears (than the ones actually driving) are disconnected from the power flow thus the slip is only a slight drag.

Attached is a partial schematic of the Getrag 7 speed in the M3 Beemer showing power flow in 1st and 2nd gears. The light blue thingies are "sliding gears" which connect the gears to the shafts when engaged. 7th gear is direct.

I have ordered the Honda manual forthe NCXD - can't wait to see how detailed it is in this area.

Kind regards,

Tapani

Thanks for that info. I stand corrected in regards to one clutch slipping most of the time. It also clears up a problem I've been struggling with about how the next gear is prepared. Simple explanations of DCT said simply that the next gear was selected and ready to engage when the clutches switch. I always wondered how the control could predict whether the next gear was up or down from the present one. Now it seams the dormant shaft is sitting in a neutral position awaiting the next change, and the gear is chosen at the start of the change process.

This also suggests that the sequential shift drum gear order on a DCT is 2-N-4-N-6 on one shaft, and 1-N-3-N-5 on the other. There is a neutral between each gear. Is that true? A conventional manual tyranny shift drum is 1-N-2-3-4-5-6.

 

[kpinvt]

Don’t expect too much from Service Manual how NC DCT works. You get better explanation online from Honda, like this:

Snipped...

To all "hard-core manual shifters" – read this newest blog. It’s about CTX700N, but experience is practically the same what with NC DCT.

Honda Worldwide | Tech Views | Vol. 1 : CTX

If you go up one level on that web site you can find links to blogs on all of the Honda DCT models:

Honda Worldwide | Tech Views | Vol. 1 : NC700X

The DCT really is a New Concept.

 

[kpinvt]

Thanks for that info. I stand corrected in regards to one clutch slipping most of the time. It also clears up a problem I've been struggling with about how the next gear is prepared. Simple explanations of DCT said simply that the next gear was selected and ready to engage when the clutches switch. I always wondered how the control could predict whether the next gear was up or down from the present one. Now it seams the dormant shaft is sitting in a neutral position awaiting the next change, and the gear is chosen at the start of the change process.

This also suggests that the sequential gear order on a DCT is 2-N-4-N-6 on one shaft, and 1-N-3-N-5 on the other. There is a neutral between each gear. Is that true? A conventional manual tyranny is 1-N-2-3-4-5-6.

Here is a quick guess on a correction to your graph above. Shouldn't there be a N before the 2 above and a N after the 5 above?

P.S.
I love this forum.

 

[670cc]

Here is a quick guess on a correction to your graph above. Shouldn't there be a N before the 2 above and a N after the 5 above?

P.S.
I love this forum.

No, I don't think that would be necessary. As long as there is an N adjacent to a gear, it doesn't matter whether the selector goes up or down to get there. I hope that makes sense.

 

[tapsak4]

I think the beemer schema illustrates all this very well. All gears are constant mesh, but are only connected to their shafts when used - one pair (drive+driven) at a time. Or to be precise one gear of each pair is not connected to its shaft when not in use. The connection is arranged with the "sliding gears" which are not really gears at all, but just collars which connect the gears to the shafts.

The basic arrangement and gear change system is very close to a "normal" motorcycle transmission. It's just the clutch system and the idea of preselection + actuator and the related control hardware which is different.

/T

 

[670cc]

I think the beemer schema illustrates all this very well. All gears are constant mesh, but are only connected to their shafts when used - one pair (drive+driven) at a time. Or to be precise one gear of each pair is not connected to its shaft when not in use. The connection is arranged with the "sliding gears" which are not really gears at all, but just collars which connect the gears to the shafts.

The basic arrangement and gear change system is very close to a "normal" motorcycle transmission. It's just the clutch system and the idea of preselection + actuator and the related control hardware which is different.

/T

Illustrates what all very well? My question about about the groove pattern on the shift fork drum. Is there a neutral position on the NC700X DCT shift fork drum(s) between each gear engagement position, whereas there is definitely not on a manual NC700X tranny's drum?

An even bigger question is, is there only one shift drum in the DCT tranny, as the illustration in post #27 suggests? If there is only one drum, preselecting the next gear while the present one is still engaged would be an interesting task.

The M3 Beemer tranny differs in that the power enter and exits in the same axis where the majority of motorcycle trannies have power enter on the input shaft and exit on the countershaft. On motorcycles, there is no "straight through gear", although there could be a "one to one" if the gear pairs had the same tooth count.

 

[tapsak4]

My question about about the groove pattern on the shift fork drum. Is there a neutral position on the NC700X DCT shift fork drum(s) between each gear engagement position, whereas there is definitely not on a manual NC700X tranny's drum?

An even bigger question is, is there only one shift drum in the DCT tranny, as the illustration in post #27 suggests? If there is only one drum, preselecting the next gear while the present one is still engaged would be an interesting task.

Sorry, I did not notice your reference to the shift drum configuration in your original post. I have no answers on the details of the NC DCT - only questions . That's why litterature explaining all this would be nice to find.

Even the first version used with the V4 engines may be a bit different from ours.

Kind regards,

Tapani

-edit: A few photos I found on the net - may or may not help. Sorry if they are reposts.

 

[tapsak4]

I humbly dare to disagree .

If you look at the last illustration in my message - I think this shows the "original position" of all gears, i.e. neutral. Non are driving. Sixth gear is free wheeling on the outer main shaft and fifth gear is doing the same on the inner main shaft. Both gears are splined on the counter shaft.

The design seems to be much more compact than the beemer schema..... third and fourth gears on the main shafts and fifth and sixth gears on the counter shaft are doing the same job as the "sliding gears" in the Getrag setup. These have cogs which are used to engage other gears to their respective shafts, but - by sliding these gears they loose mesh to their own partners.

The shift drum is still to be seen.....

/Tapani

 

[tapsak4]

This could be of interest. Unfortunately I am not able to go thru it in detail tonight - it's 8:30 pm and I need concentrate on other stuff.

The patent drawings are always far from the real thing..... though the primary driven gear appears to be between the two clutches - like in the NC.

Patent EP1967771A1 - Automatic transmission assembly for a vehicle, and vehicle incorporating same - Google Patents

/T

 

[Bert]

This could be of interest./T

Looks very familiar. And it's also for Honda, this is projected to be in an ATV and single cilinder. But the rest looks the same. Even the way the gears are supposed to work agree with what i've heared/felt in mine.

 

[670cc]

The shift drum pattern is the secret decoder ring to the whole process.

Questions to answer:

1) If two gears are in fact always engaged at one time, it means one clutch always slips all the time. Is that good?

2) If two gears are engaged at one time, then the TCU has predicted whether the next change is going to be up or down. At such time if I decide to downshift with the paddle when the TCU was expecting to up shift, then the prediction was wrong and extra steps would be needed to do the downshift. That seems inefficient.

I'm beginning to think that the shift drum, assuming there is only one, has a more complex grove pattern than includes neutrals between each gear and requires two rotary steps for each gear change. Process: Assume bike is moving forward in some gear on shaft B. To shift up or down, first step drum to engage the next requested gear on shaft A, allow clutches to swap power flow to shaft A, step again to disengage all gears for shaft B. Clutch B can now be engaged, OR could remain disengaged but oil drag would make it spin anyway. No gears are engaged on shaft B so it wouldn't matter. However, leaving clutch B disengaged would prepare the tranny for the next gear change. Having the shift drum operate in this manner means it rotates one way two steps for up shifts, the other way two steps for downshifts. This would be like the manual transmission, but on the manual one gear is disengaged and the other is engaged all in one drum rotation step.

 

[Normsthename]

Very interesting!
It's good that it just works!

Andy

 

[maxwellian]

I don't know about the neutral thing,

But as far as one clutch "slipping" all the time, isn't the oil drag between the disengaged clutch's plates the source of decreased efficiency? It wouldn't cause wear on anything except maybe thrust bearings though. And don't thrust bearings last forever on a wet clutch?\

It also seems like the smooth shifting of the DCT has to be easier on the parts up and downstream of the transmission.

 

[670cc]

Let’s go back to original subject of this thread:
These DCT gearboxes are all the rage you know!

Here is description for 2015 Honda Acura TLX:

"Sequential SportShift 8-Speed Dual-Clutch Transmission (DCT) with Torque Converter.

The ultra-thin torque converter complements the efficient operation of the DCT by providing exceptionally smooth operation in stop-and-go situations, plus it offers off-the-line torque multiplication for improved initial acceleration that a DCT alone can't equal. In an aggressive standing-start launch, the torque converter substantially improves acceleration in the first 1.4 seconds, or about the first 60 feet (as compared to a DCT alone)."[/I]

Interesting. The car has a torque converter as well. So, a torque converter plus two clutches? Sounds like just an automotive automatic tranny with a parallel shaft gear arrangement instead of planetary gears.

 

[Bert]

I don't know about the neutral thing,

But as far as one clutch "slipping" all the time, isn't the oil drag between the disengaged clutch's plates the source of decreased efficiency? It wouldn't cause wear on anything except maybe thrust bearings though. And don't thrust bearings last forever on a wet clutch?\

It also seems like the smooth shifting of the DCT has to be easier on the parts up and downstream of the transmission.

As far as one clutch always slipping. The force transferred by the slipping is also tranferred to something attached to the driveline/engine. So losses would be minimum compared to losses against something standing still.